Investors & landlords

He would have to report the form 1099-B information as it is listed on the form. When he goes to enter it in TurboTax, he will see this screen:

He needs to click on the "I'll enter additional info on my own" tab and that will allow him to enter a new cost basis for the sale, equal to the one listed on the 1099-B form, plus your share of the gain on sale. That will result in an adjustment on his tax return to reduce his gain for your share of it.

On your tax return, you will go to the "Investment Income" section and find "Stocks, Mutual funds, Bonds, Other" and indicate that you do not have a form 1099-B, and you will see this screen:

Choose the "Stock" option and enter your gain as the sale amount and leave the basis empty.